1. Field of the Invention
The present invention relates to an IP communication method, an IP terminal apparatus, an ENUM server and an IP communication system, especially relating to the IP communication method that includes the IP terminal apparatus and the ENUM server, the IP terminal apparatus, the ENUM server and the IP communication system.
2. Description of Related Art
With rapid spread of the Internet these days, an IP telephone system draws attention since the system allows low-rate calls to a telephone apparatus in a remote location and free calls between IP telephone apparatuses of subscribers. A protocol “ENUM (Telephone Number Mapping),” provided in RFC2916 (Publication 1) that the IETF (Internet Engineering Task Force) and the ITU-T (International Telecommunication Union—Telecommunication Standardization Sector) have been developing, is used to connect services and resources on the Internet with telephone numbers.
Based on a DNS (Domain Name System) architecture, the “ENUM” protocol retrieves IP addresses or URI's (Uniform Resource Identifier) using telephone numbers converted to meet the E.164 system defined by the ITU-T.
[Publication 1] The first report of ENUM Trial Japan issued by ENUM Trial Japan in May, 2004
However, an ENUM server that connects to an IP communication system is an open system being accessible via DNS, thus vulnerable to security problems, including a possibility that a third party may capture a packet communicated between an IP terminal apparatus and the ENUM server.
NAPTR (the Naming Authority Pointer) resource records registered on the ENUM server are configured based on a telephone number. Therefore, when a plurality of telephone numbers are used to inquire NAPTR resource records on the ENUM server, it is possible to gather the NAPTR resource records corresponding to the plurality of telephone numbers. Then, the gathered NAPTR resource records could be used to gather user information set up on IP terminal apparatuses, posing a problem that user information could be leaked to a third party.